Printed circuit boards represent today a very substantial and rapidly growing market. They can be used, for example, in communications, instruments, controls, military, aerospace and business applications. Printed circuit boards other than copper clad laminates are typically manufactured by plating an epoxy or phenolic compound or some other heatstable dielectric resin with a conductive metal such as, for example, copper. It is also known to plate flexible films of polyester and polyimide for this purpose. The successful production of printed circuit boards is a complex and sophisticated art that, though rapidly advancing, has yet to pass beyond the adolescence of its evolution.
Processing techniques known in the art include methods commonly identified as the subtractive method, the semiadditive method, the additive method and modifications and variations of the above. Electroless plating of the board (i.e. epoxy resin, phenolic resin, etc.) with a conductive metal is a crucial part of the overall process. After electroless deposition of a layer of the conductive metal onto the board the board is typically further plated with more of the conductive metal in accordance with conventional electroplating techniques to increase the thickness of the layer.
Absolutely essential to the success of the finished product is good adhesion of the conductive metal (which after processing represents the circuitry) to the board (i.e. epoxy resin, phenolic resin, etc.). In the absence of satisfactory adhesion the circuitry loses its structural integrity and the printed circuit board fails to perform its intended function. Those of skill in the art seek to discover new materials which can be used in the manufacture of printed circuit boards. The challenge is to find materials which will give good adhesion and yet possess other attributes (such as, for example, high temperature resistance) that are needed in printed circuit boards.
Poly(phenylene sulfide) is a material which possesses many of these desired attributes (such as, for example, high temperature resistance) but to the limited extent it has been considered at all it has been rejected by those of skill in the art as a material suitable for printed circuit board application, the belief being that satisfactory adhesion of the conductive metal to the poly(phenylene sulfide) cannot be obtained.